1. Field of the Invention
The present invention relates to a lens barrel, and in particular, to a lens barrel having a rotatable cylindrical ring with a curvilinear cam groove or slot and a stationary cylindrical ring with a linear cam groove or slot which are arranged coaxially with each other and a lens holder with a cam follower pin in engagement with both curvilinear cam groove and linear cam groove so as to move linearly along the linear grooved cam following movement of the curvilinear grooved cam when rotating either one of the rotatable cylindrical rings relative to the other.
2. Description of the Related Art
Typically, there are numerous lens barrel s that drive optical lens elements, such as a zooming lens element and a focusing lens element, by an manually operated ring or a motor driven ring. Such a lens barrel comprises at least a cylindrical ring with a linear cam groove or slot (which is referred to as a cylindrical linear cam ring) in which lens holders holding focusing lens elements or zooming lens elements is installed and a cylindrical ring with a curvilinear cam groove or slot (which is referred to as a cylindrical curvilinear cam ring) that is fitted externally on and coaxialy with the inner cylindrical ring. These cylindrical cam rings are configured such that either one of the cylindrical cam rings rotates relatively to the other. The lens holder is provided with a cam follower pin which extends radially into the curvilinear cam groove of the cylindrical curvilinear cam ring passing through the linear cam slot of the cylindrical linear cam ring. The lens barrel thus constructed moves the lens holders in an axial direction following rotation of either the cylindrical linear cam ring or the cylindrical curvilinear cam ring.
The this type of lens barrel restricts these cylindrical cam rings in axial position relative to a stationary cylindrical ring of the lens barrel by means of a restrictive ring or a restrictive plate while allowing them to rotate about the optical axis. This construction of the lens barrel has a drawback in an increase in cost that is induced by a large number of parts and an increased man-hour for assembling the lens barrel.